To determine the approximate speed of the stone at the point where it turns back to the ground, we need to consider the motion of the stone and the forces acting on it.
Assuming negligible air resistance and considering the stone's motion in a vertical plane, we can analyze its trajectory using the principles of projectile motion.
When the stone is thrown towards the flying bird, its initial vertical velocity is zero since it is thrown horizontally. However, it has an initial horizontal velocity of 20 m/s.
As the stone moves upward, it experiences a gravitational force acting downward, causing it to slow down until it reaches its highest point where its vertical velocity becomes zero. At this highest point, the stone starts to descend back towards the ground.
The magnitude of the vertical velocity of the stone at the point of turning back to the ground would be the same as its initial magnitude but in the opposite direction, assuming we neglect air resistance. Therefore, the vertical component of the velocity will be -20 m/s.
To find the total speed at this point, we need to combine the horizontal and vertical components of velocity using the Pythagorean theorem.
Magnitude of the velocity at the point of turning back = √[(horizontal velocity)² + (vertical velocity)²] = √[(20 m/s)² + (-20 m/s)²] = √[400 m²/s² + 400 m²/s²] = √(800 m²/s²) = √800 m/s ≈ 28.3 m/s (rounded to one decimal place)
Therefore, the approximate speed of the stone at the point where it turns back to the ground is approximately 28.3 m/s.